Internal combustion engines

ABSTRACT

An internal combustion engine includes one or more pistons ( 4 ), each of which is mounted to reciprocate in a respective cylinder ( 2 ) and is pivotably connected to a connecting rod ( 6 ) which is connected to a respective crank on a crankshaft ( 7 ). The connecting rod ( 6 ) is pivotably connected to one end of an elongate link ( 14 ), which is pivotably connected to the associated crank at a point intermediate its ends and whose other end constitutes a rod ( 18 ) which is restrained by a mounting ( 20, 24 ) such that it may pivot about a pivotal axis parallel to the axis of the crankshaft. The mounting includes a first movable mounting member ( 20 ) and a second movable mounting member ( 24 ). The first mounting member ( 20 ) is connected to the rod ( 18 ) by a connection which permits only relative sliding movement in the direction of the length of the rod and is pivotally connected to the second mounting member ( 24 ) to pivot with respect thereto about the said pivotal axis. A single actuator ( 30 ) is provided which cooperates with the second mounting member ( 24 ) and is arranged to move it. The second mounting member ( 24 ) is an elongate lever which is connected to a fixed structure to pivot with respect thereto about an axis substantially parallel to the axis of crankshaft.

The present invention relates to internal combustion engines of the typein which the compression ratio and the swept volume may be alteredduring operation of the engine. More specifically, the invention relatesto internal combustion engines including one or more pistons, each ofwhich is mounted to reciprocate in a respective cylinder and ispivotally connected to a connecting rod which is connected to arespective crank on a crankshaft, the connecting rod being pivotallyconnected to one end of an elongate link member which is pivotablyconnected to the associated crank at a point intermediate its ends andwhose other end constitutes a rod which is restrained by a mounting suchthat it may pivot about a pivotal axis parallel to the axis of thecrankshaft, the mounting including a first movable mounting member and asecond movable mounting member, the first movable mounting member beingconnected to the rod by a connection which permits only relative slidingmovement in the direction of the length of the rod and the first movablemounting member being connected to the second movable mounting member tobe pivotable with respect thereto about the said pivotal axis, a singleactuating means being provided which cooperates with the second movablemounting member and is arranged to move it.

Such an engine is disclosed in EP-B-0898644. In the engine disclosed inthis patent, the first mounting member comprises a sleeve or the likewhich slidably retains the rod of the link member and is pivotallyconnected to the second mounting member which is selectively movable byan actuator in a direction parallel to the axis of the associatedcylinder. Movement of the first mounting member in this directionresults primarily in a change in the top dead centre position of thepiston and thus in the compression ratio, though also in a small changein the bottom dead centre position of the piston and thus in the strokeof the piston.

It is, however, often desirable to be able to make a substantial changeto the stroke of the piston and thus to the swept volume of the engineand to this end EP-B-1012459 discloses a modified engine which includestwo actuators. The first actuator is arranged to move the first mountingmember parallel to the cylinder axis, and thus changes the compressionratio of the engine, and is carried by the second actuator, which isarranged to move the first actuator and thus the first mounting memberperpendicular to the cylinder axis and thus changes the stroke of thepiston and thus the swept volume of the engine. The engine ofEP-B-1012459 thus enables the compression ratio and the swept volume ofthe engine to be changed at will independently of one another.

However, the inclusion of a second actuator in the engine ofEP-B-1012459 adds not inconsiderably to its structural complexity andcost and also to the complexity of the control system that is required.Although the engine may be operated with any desired combination ofvalues of compression ratio and swept volume within the ranges that maybe obtained, it is now appreciated that this is in fact not necessary inall cases. Thus at relatively low speed and/or load a relatively smallswept volume and a relatively high compression ratio are desirablewhilst at relatively high speed and/or load a relatively large sweptvolume and a relatively low compression are desirable. Although theactuators are able to position the mounting so that a large swept volumeis provided in combination with a high compression ratio and also asmall swept volume in combination with a low compression ratio, theseoperating configurations may in practice rarely be required.

It is in practice necessary, in connection with the engines disclosed inthe prior patents referred to above, to provide an extension to thecrankcase which constitutes a housing for the actuator system beside theengine roughly at the level of the crankshaft. In practice, some vehicleengine compartments and space constraints may render the provision ofsuch a structure difficult.

It is, therefore, the object of the invention to provide an engine ofthe type referred to above which has the advantage of being able toadjust both the compression ratio and the swept volume but with reducedcomplexity and hence cost.

According to the present invention, the second movable mounting memberis an elongate lever which is connected to a fixed structure to pivotwith respect thereto about an axis substantially parallel to the axis ofthe crankshaft.

Thus in the engine in accordance with the invention, the mounting forthe elongate bar comprises a sleeve or the like which slidably retainsthe bar within it and is pivotally connected to an elongate lever, whichis also pivotally connected to a fixed structure. The actuatorcooperates with the elongate lever and can move it only in rotationabout its pivotal axis. This necessarily means that the first mountingmember is moved not linearly but over an arcuate path. Movement alongthis arcuate path may be resolved into movement perpendicular to theaxis of the cylinder and movement parallel to the axis of the cylinderand thus operation of a single actuator will result in both thecompression ratio and the swept volume of the engine changing. Theprecise ratio of movement perpendicular and parallel to the cylinderaxis between the end points of the arcuate path may be varied inaccordance with requirements by altering the length of the elongatelever and the position of its pivotal mounting.

As mentioned above, it has been appreciated that it may not be necessaryto provide a full range of combinations of compression ratio and sweptvolume and the invention is based on the recognition that if one plotsthe combinations of compression ratio and swept volume which areactually useful in practice on a graph of compression ratio againstswept volume, the various points lie for many engines on a generallyarcuate line. By appropriately dimensioning the elongate lever andpositioning its pivot point, the first mounting member can be caused tomove along an arcuate path which corresponds in qualitative terms to thearcuate line referred to on the graph above. This means that byproviding a pivotally mounted elongate lever, it is possible for themounting to be adjusted to obtain substantially all the combinations ofcompression ratio and swept volume that are in practice normallyrequired using only a single actuator.

The actuator, which is preferably a linear actuator, preferably actsdirectly on the elongate lever. Thus in the preferred embodiment, theelongate lever is rotatably carried by a shaft mounted in fixedmountings and the actuator acts on the lever to rotate it with respectto the shaft.

However, in an alternative embodiment the elongate lever isnon-rotatably mounted on an actuator shaft which is rotatably mounted infixed mountings, i.e. bearings, and the actuator acts on the shaft torotate it. In this case, the actuator may be a rotary actuator whichacts directly on the actuator shaft but it is preferred that the engineincludes an actuator lever which is also non-rotatably connected to theactuator shaft and that the actuator acts on the actuator lever, inwhich case the actuator may again be of linear type. Thus the actuatorshaft may be of non-circular section, e.g. hexagonal, splined or thelike, and the elongate lever and the actuator lever, if provided, willthen have a hole in one end whose shape corresponds to that of theactuator shaft. Movement of the free end of the actuator lever will thenresult in rotation of the actuator shaft within its fixed mountingswhich will in turn result in pivotal movement of the elongate lever andthus movement of the first movable mounting member along an arcuatepath.

It is likely that the actuator will be of active or positive type, thatis to say of the type which is powered, e.g. electrically orhydraulically and actively causes the elongate lever to move pivotallyabout its mounting axis. However, this may not be essential and in afurther embodiment the actuator is of negative or passive type, that isto say it does not actively cause the elongate lever to move but insteadmerely permits it to move. In this embodiment, the actuator is thereforemore in the form of a selectively releasable lock. Thus tests have shownthat the elongate rod exerts substantial fluctuating moments on themounting and these moments tend to cause pivotal movement of theelongate lever in one direction and then in the other directionalternately. It is therefore possible to make use of these moments ortorques by locking the mounting in position and releasing it at the timeat which it is desired to move the elongate lever in a specificdirection. This may be done by sensing when the torque is tending tocause the elongate lever to move in that direction and then releasingthe releasable lock to permit the desired movement to occur, whereafterthe releasable lock is reapplied. In practice, it may not be possiblefor all of the desired movement of the elongate lever to occur in asingle continuous movement because the torque applied to it fluctuatesand reverses very rapidly and it may therefore be necessary for thereleasable lock to be released on each of a number of successiveoccasions when the torque acting on it is acting in the correctdirection and reapplying the lock at times between those occasions,whereby the elongate lever will move incrementally until it has reachedthe desired position.

It is, however, preferred that the actuator is constructed to operate inthe manner of a ratchet and is selectively switchable to preventmovement of the second movable mounting member or to permit movement ina selected one of two directions whilst preventing movement in theopposite direction. The advantage of this construction is of course thatit is not necessary to detect when the forces acting on the secondmovable mounting member are acting in a particular direction and theselectively operable lock is merely effectively unlocked in one selecteddirection but maintained locked in the other direction. This will meanthat the selective lock will permit movement of the second movablemounting member in the desired direction each time the forces acting onit act in that direction but will prevent movement in the oppositedirection. A sensor will determine when the desired amount of movementhas occurred and the selectively operable lock will then be fully lockedagain until some further movement is required.

In one specific embodiment, the actuator includes a hydraulic cylinderaccommodating a piston connected to the second movable mounting member,the piston dividing the cylinder into two chambers filled with hydraulicfluid, the two chambers communicating via two conduits, each of whichincludes a non-return valve and a control valve which is selectivelyoperable to permit the piston to be moved by the forces acting on it ina predetermined direction.

Actuation of the positive actuator or release of the selectivelyreleasable lock will of course be controlled by a central controlsystem, e.g. incorporated in the engine management system, which is nowconventionally provided on automotive engines, in response to signalsproduced by a number of sensors indicative of, amongst other things,engine load, engine speed, position of the crankshaft and the like.

Further features and details of the invention will be apparent from thefollowing description of three specific embodiments which is given byway of example only with reference to the accompanying diagrammaticdrawings, in which:

FIG. 1 is a schematic view of the first embodiment showing only a partof a multi-cylinder four-stroke engine in accordance with the inventionwith the mounting shown in the position in which the engine has a lowcompression ratio and a high capacity or swept volume;

FIG. 2 is a similar view of the second embodiment;

FIG. 3 is a similar view of the second embodiment but with the mountingin the position in which the engine has a high compression ratio and alow capacity or swept volume; and

FIG. 4 is a diagrammatic view of the passive actuator or selectivelyreleasable lock used in the embodiment of FIG. 2.

In the embodiment of FIG. 1, the engine has four cylinders, though itmay have more or less than this or even only a single cylinder, but onlya single cylinder 2 is shown. All those features of the engine which arewholly conventional and form no part of the present invention, such asthe cylinder block, the cylinder head, the inlet and outlet valves andthe spark plug are shown only in chain lines and will not be describedin detail. Reciprocably mounted in the cylinder is a piston 4. Thepiston is pivotally connected about an axis 5 in the usual manner to aconnecting rod 6. Extending below each cylinder 2 is a crankshaft 7,which carries a respective crank or crank throw 9 for each piston. Theconnecting rod 6 is not directly connected to the associated crank butinstead pivotally connected about an axis 12 to one end 11 of arespective elongate link 14. which has two portions inclined to oneanother by about 120°. The link is also pivotally connected at a pointintermediate its ends to the associated crank 9. The other end 18 of thelink 14, which is in the form of a bar, is longitudinally slidablyreceived in a mounting. The bar 18 may be of circular section, in whichevent it may be hollow, or it may be cut away for weight-savingpurposes, in which case it may be generally of I cross-section orcruciform cross-section, with webs defining an outer surface ofsubstantially circular shape to facilitate longitudinal sliding andlateral force transfer.

The mounting includes a first movable mounting member 20, which isconstituted by a sleeve defining a hole or passage through which the bar18 passes and is slidably retained therein. The sleeve 20 isaccommodated in the space between and pivotally connected to the twolimbs 22 of a respective bifurcated mounting lever 24 at a pointintermediate its ends. The sleeve 20 may thus pivot or rotate withrespect to the lever 24 about an axis which is parallel to the axis ofthe crankshaft. One end of the lever 24 has a hole of circular shape inwhich a complementarily shaped stationary shaft 26, attached to thecylinder block, is rotatably received. The other end of the lever 24 isconnected to a positive actuator, in this case a linear hydraulicactuator 30. Extension or retraction of the actuator 30 will result inrotation of the lever 24 about the shaft 26. The sleeve 20 is thuscaused to move over an arcuate path.

In use, the engine operates in substantially the same manner as thatdisclosed in EP-B-1012459, to which reference should be made. Duringsteady state operation of the engine, the bar 18 reciprocates linearlywithin the sleeve 20 and the sleeve 20 reciprocates in rotation aboutits pivotal connection with the lever 24. If the engine is operating athigh speed and/or under high load, the mounting is held in the positionshown in FIG. 1 in which the compression ratio is relatively low and theswept volume of the engine is high. If, however, the speed and/or loadshould drop, this is sensed by various sensors and the engine managementsystem then issues a signal to the actuator to move the mounting intothe position shown in FIG. 3 in which the compression ratio isrelatively high and the capacity of the engine relatively low. Theengine management system can be programmed to move the mountingprogressively between its two end positions or alternatively it may beprogrammed to switch the mounting between the two end positions or toswitch it incrementally between any predetermined number of setpositions. The second embodiment illustrated in FIG. 2 is very similarto that illustrated in FIG. 1 and differs from it in that the actuator30 does not act directly on the lever 24. In this case, the shaft 26 isnot stationary but constitutes an actuator shaft and one end of thelever 24 has a hole of non-circular shape in which the complimentarilyshaped actuator shaft 26 is non-rotatably received. The actuator shaftis retained at its two ends by stationary bearings, e.g. mounted on theside of the cylinder block, and thus cannot move linearly but is mountedto rotate about its own axis in the bearings. Also connected to theactuator shaft 26 is an actuator lever 28, which is again non-rotatablewith respect to the shaft 26. Connected to the free end of the actuatorlever 28 is a positive actuator, in this case a linear hydraulicactuator 30, which can actively move the lever 28 and thus turn theshaft 26. Extension or retraction of the actuator will result inrotation of the shaft 26 about its axis and thus in rotation also of thelever 24 about the axis of the shaft 26. The sleeve 20 is thus againcaused to move over an arcuate path.

FIG. 3 also illustrates the third embodiment which is essentially thesame as the first embodiment except that the active actuator 30 isreplaced by a passive actuator 32 or selectively operable brake whichcan not actively move the lever 24 but can be selectively released topermit the lever 24 to be moved, that is to say rotated by thefluctuating torques which act on it. In this case, the actuator 32 isconstructed to operate in the manner of a ratchet, that is to say it maybe switched to permit movement of the lever 24 under the forces actingon, it in a selected direction but to prevent movement in the oppositedirection.

FIG. 4 is a detailed diagrammatic view of the passive actuator 32. Itagain consists of a hydraulic cylinder 34, in which is a piston 36, thepiston rod 38 of which is pivotally connected to the end of the lever24. The piston divides the cylinder into two spaces 40, 42, which arefilled with hydraulic fluid. The two spaces 40, 42 are connected by afirst conduit 44, which includes a first control valve 46 and a firstone-way valve 48, and by a second conduit 50, which includes a secondcontrol valve 52 and a second one-way valve 54. Both conduits 44 and 50also communicate with an unpressurised source, which is typicallyunpressurised, of hydraulic fluid via respective conduits 56, 58 so thatany leakage is compensated for.

If it is desired to move the piston rod 38 to the left, as seen in FIG.4, the engine management system opens the control valve 46. Fluid isthen displaced, each time there is a force acting on the piston rodtending to move it to the left, from the space 40 via the valves 46 and48 into the space 42 until the desired amount of movement has occurredand the valve 46 is then closed, whereafter the actuator ishydraulically locked. If it is desired to move the piston rod to theright, the same procedure is adopted but in this case the control valve52 is opened. It will be appreciated that the purpose of the non-returnvalves is to prevent the piston being moved by the action of the reverseforce acting on it when one or other of the control valves is open.

In the embodiment of FIGS. 3 and 4, the passive actuator 32 acts on thelever 24 in the same manner as the positive actuator 30 in theembodiment of FIG. 1. It would, however, also be possible for thepassive actuator to act on an actuating lever 28 in the manner shown inFIG. 2 or to act directly between the lever 24 and the shaft 26 so as toselectively permit or prevent rotation of the lever 24 about the shaft26. Numerous other modifications could readily be devised.

1. An internal combustion engine including one or more pistons, each ofwhich is mounted to reciprocate in a respective cylinder and ispivotally connected to a connecting rod which is connected to arespective crank on a crankshaft, the connecting rod being pivotallyconnected to one end of an elongate link member which is pivotablyconnected to the associated crank at a point intermediate its ends andwhose other end constitutes a rod which is restrained by a mounting suchthat it may pivot about a pivotal axis parallel to the axis of thecrankshaft, the mounting including a first movable mounting member and asecond movable mounting member, the first movable mounting member beingconnected to the rod by a connection which permits only relative slidingmovement in the direction of the length of the rod and the first movablemounting member being connected to the second movable mounting member tobe pivotable with respect thereto about the said pivotal axis, a singleactuating means being provided which cooperates with the second movablemounting member and is arranged to move it, characterised in that thesecond movable mounting member is an elongate lever which is connectedto a fixed structure to pivot with respect thereto about an axissubstantially parallel to the axis of the crankshaft.
 2. An engine asclaimed in claim 1 in which the elongate lever is rotatably carried by ashaft mounted in fixed mountings and the actuator acts on the lever torotate it with respect to the shaft.
 3. An engine as claimed in claim 1in which the elongate lever is a non-rotatably connected to an actuatorshaft which is rotatably mounted in fixed mountings, and the actuatoracts on the shaft to rotate it.
 4. An engine as claimed in claim 3including an actuator lever which is non-rotatably connected to theactuator shaft and the actuator acts on the actuator lever.
 5. An engineas claimed in claim 1 in which the elongate lever is bifurcated andcomprises two arms between which the first movable mounting member isreceived and to which the first movable mounting member is pivotallyconnected.
 6. An engine as claimed in claim 1 in which the actuator isof positive type and is arranged positively to move the second movablemounting member.
 7. An engine as claimed in claim 1 which the actuatoris of passive type and constitutes a selectively releasable lock whichmay be released to permit the second movable mounting member to be movedunder the action of the forces exerted on it by the rod.
 8. An engine asclaimed in claim 7 in which the actuator is constructed to operate inthe manner of a ratchet and is selectively switchable to preventmovement of the second movable mounting member or to permit movement ina selected one of two directions whilst preventing movement in theopposite direction.
 9. An engine as claimed in claim 8 in which theactuator includes a hydraulic cylinder accommodating a piston connectedto the second movable mounting member, the piston dividing the cylinderinto two chambers filled with hydraulic fluid, the two chamberscommunicating via two conduits, each of which includes a non-returnvalve and a control valve which is selectively operable to permit thepiston to be moved by the forces acting on it in a predetermineddirection.